The CTK-860IN is one of the newer boards that will take up to a 32 Gb SD Card, but if you are trying to use one of the newer 64 Gb or larger cards, then those will not work. 32 Gb is max for the 860IN! If that is not the problem, check the write protect switch on the side of the card to see if it got turned on somehow. If you are not familiar with this: when you hold the card with the cut off corner to your upper right, the write protect switch is on the opposite edge. It should be slid as far upward as possible. If it has been slid downward, then it is write protected, and you will not be able to format it. A computer will normally tell you exactly that, but the keyboard will just tell you that the format failed. The SD Card slot on my computer here is getting a bit sloppy, and if I kant the card a bit to the left as I insert it, it slides the switch to the write protected position, and I get an unpleasant surprise. Even though the card should be formatted in the keyboard, there is nothing wrong with plugging it into a computer's SD Card slot to run diagnostics on it with the computer's operating system.